You should always learn something new every day. That's why my parents always tell me to read a book, study something new, do something new to nourish your brain. Never stop learning.
One new thing that I have learned is to do layouts with Adobe Indesign. It's sounds hard at first but eventually with books, you will learn it.
When you create a new document, the default size is in picas. As a rule of thumb.
6 picas = to one inch
So depending the document size, just compute it by multiplying the inches with the "6", then you will arrive at the right number of picas.
Hope this helps.